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  1. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Inferno, There is not a modified schematic, but I posted a modified Parts List and instructions that should work well. If you short its output then it will switch to current-regulation and supply the set current (of its current control pot) to the short. If the current setting is high, then...
  2. audioguru2

    Electronic Stethoscope

    Hi again, Another discussion about how a heartbet looks like was here: http://www.electronics-lab.com/forum/index.php?board=22;action=display;threadid=1274
  3. audioguru2

    Electronic Stethoscope

    Hi Prateek, The simulator shows an amplitude-modulated kind of envelope because the microphone picks-up the hearbeat sound through the air, and feeds it to the circuit through a capacitor. This circuit won't produce a DC single-polarity pulse like a DC-coupled ECG. The output of a professional...
  4. audioguru2

    In circuit transistor tester

    Hi Hotwaterwizard, Your 1st and 2nd transistor tester circuits are great and easy to make. Sorry, but in the 3rd one, it tests the two transistor junctions separately, not like a transistor that normally has a reversed-biased C to B junction. Without any current-limiting, the transistor's base...
  5. audioguru2

    switching circuit

    Hi MP, Actually, I used the pun on the word,"bit" on purpose. With the micro using only an 8-bit ADC, the LSB is 19.5mV. If the 12V battery (up to 15V) is scaled to a 5V range, then when its charging voltage drops one bit (LSB), the battery is already overcharging. That is why some charger...
  6. audioguru2

    Electronic Stethoscope

    Hi Emad, Welcome to our forum and greetings to Egypt. The negative power supply terminal is not connected to ground. The 0V junction of the positive and negative power supplies connect to the project's "ground" points at many locations on the schematic, including the shield of the cable to the...
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Inferno, Welcome to our forum. 1) The project's schematic doesn't show it, but the PCB and pinout of the TL081 show that RV1 connects between pin 1 and pin 5 of U2, which is called Null, Balance or Offset Voltage Adjustment. 2) Yes, the emitter of Q1 should connect to the project's 0V...
  8. audioguru2

    switching circuit

    Hi again, I'm glad to help you. Your 12V NiCd will reach a voltage of nearly 15V just before it is fully charged, then the voltage will drop a bit when it actually is fully charged and begins getting hot. Is your micro going to detect that small voltage drop? Most commercial "fast" chargers use...
  9. audioguru2

    Notch Filters and Noise Cancellers

    Hi Adam, I found an "ultimate" audio comb filter project for you. It even has measurement results and some mp3 demos. It really works well! Although designed to remove a tone, its author says how to easily change its comb frequencies. The project is here...
  10. audioguru2

    switching circuit

    Hi Mphotis, You have Ohm's Law backwards. A single resistor passes a current depending on the resistor's value (ohms) and the voltage across it. A resistor that is in parallel will create a lower resistance (since each one passes its own current), and therefore together they will pass a higher...
  11. audioguru2

    In circuit transistor tester

    Hi Steven, Yes, I understand that a transistor that is good will turn-off its blinking LED. But I think that your transistor tester will also show that a faulty transistor with a very low gain is good. To simulate a transistor that has a very low gain, please test a good BC548, 2N3904 or 2N2222...
  12. audioguru2

    In circuit transistor tester

    Hi Steven, Yeah, that's a good one. Is that a solid metal case? I have heard that many transistors have some gain when their emitter and collector leads are backwards. What does your tester do then? Does the LED dim only a bit or completely?
  13. audioguru2

    Transistor tester

    Hi Steven, That's a good looking kit and it has a strong case. I also like your grip clip thingys. I had some that got worn out, but I haven't replaced them yet because I can't figure out how to take apart the new ones.
  14. audioguru2

    0-30 Vdc Stabilized Power Supply

    R10 is part of an offset voltage adjustment for U2 (0V adjustment), and is not an input. R12 is the feedback resistor that would connect to your remote sense, instead of to the local output. But R12 connects directly to U2's input, which has a very high gain.
  15. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Dkilshaw, I think that it will oscillate and pickup interference if you use long feedback wires for remote sensing. This circuit has a very high open-loop gain of about 75,000, so only 13uV (!) of noise pickup will make 1V in its output.
  16. audioguru2

    Transistor tester

    Hi Steven, Your transistor multivibrator is the same basic circuit as this project that uses ICs. The transistor being tested shorts its LED. Just think how poorly it would work if one transistor's emitter wasn't grounded so that it wouldn't oscillate, just like this faulty project. I like...
  17. audioguru2

    Notch Filters and Noise Cancellers

    Hi Adam, Something must be arcing underground. Just hope that it completely fails soon, then they will have to fix it. Of course, the interference is RF, and that your AM longwave tuner outputs it as 120Hz hash. Like I said earlier, a notch filter won't remove the harmonics, which is the hash...
  18. audioguru2

    Flickering dimmer switch

    Ah-ha, Don't "ordinary" dimmers say on them "not for use on transformer powered low-voltage lights"? I think that "special" dimmers are made for that purpose. The inductance of the transformer will screw-up the phase control at low settings and cause flickering. Hi Steve, Don't use your "mains"...
  19. audioguru2

    Transistor tester

    MP, The only modification that was successfully done to this project was when Mozikluv replaced its 555 and 4027 with a 4093, similar to Steven's transistor multivibrator. Mixos posted a successful "change" in bold red lettering that was to connect the ground (pin 8) pin of the 4027 to ground...
  20. audioguru2

    Transistor tester

    Steven, your circuit is very similar to this one. This project's corrected schematic is here:
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